The present invention relates to automotive vehicles, and more particularly to powertrain control of automotive vehicles.
A vehicle powertrain typically includes a power source, such as an internal combustion engine, coupled to a gearbox, such as a transmission with various gear ratios. A powertrain controller is usually provided which controls the powertrain in part based on a driver""s requests.
In one system, desired powertrain output is determined based on depression of a pedal by a vehicle operator. In such a system, a strategy is needed for the situation when a driver releases the pedal, known to those skilled in the art as a tip-out. During a tip-out, the driver is indicating a desire for reduced engine output. Further, a strategy is needed for the situation when a driver depresses the pedal, known to those skilled in the art as a tip-in. During a tip-in, the driver is indicating a desire for increased engine output.
The inventors herein have recognized a disadvantage if conventional methods of powertrain output control are used during tip-out and tip-in situations. In particular, if the accelerator pedal is released and subsequently engaged, poor drivability may be experienced due transmission gears lash. For example, when the engine transitions from exerting a positive torque to exerting a negative torque (or being driven), the gears in the transmission separate at the zero torque transition point. Then, after passing through the zero torque point, the gears again make contact to transfer torque. This series of events produces an impact, or clunk, resulting iII poor drivability and customer dissatisfaction. In other words, the engine first exerts a positive torque through the torque converter onto the transmission input gears to drive the vehicle. Then, in response to the driver tip-out, the engine is driven by the torque from the transmission through the torque converter. The transition between these two modes is the point where the engine is producing zero engine brake torque. Then, at this transition point, the gears in the transmission separate because of inevitable transmission gear lash. When the gears again make contact, they do so dynamically, resulting in an undesirable impact.
This disadvantage is exacerbated when the operator returns the accelerator pedal to a depressed position, indicating a desire for increased powertrain output. In this situation, the zero torque transition point must again be traversed. However, in this situation, the engine is producing a larger amount of torque than during deceleration because the driver is requesting acceleration. Thus, another, more severe, impact is experienced due to the transmission lash during the zero torque transition.
Disadvantages of prior approaches are overcome by a method for controlling a powertrain of a vehicle, the powertrain having a transmission. The method comprises determining whether torque transmitted through the transmission is within a predetermined torque range; and adjusting an engine control signal to limit a change in powertrain output when it is determined that torque transmitted through the transmission is within said predetermined torque range.
By limiting a change in powertrain output when transmitted torque is within a predetermined range, it is possible to provide improved drive comfort with minimimal impact on performance feel. In other words, limiting the change in torque minimizes the effects of transmission gear separation, or xe2x80x9cclunkxe2x80x9d. However, since torque can be limited only under conditions where transmission gear separation occurs, other driving conditions are not hindered by any torque limitations.
It is important to note that there are various methods to determine whether transmitted torque is within a predetermined torque range. For example, this can be judged by observer torque converter input and output speeds of an unlocked torque converter. Similarly, it can be done using estimates of engine output torque. Similarly, various engine control signals can be used, such as engine air flow, engine air/fuel, ignition timing, or throttle angle.